view tests/test-bookmarks-strip.t @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "mq=" >> $HGRCPATH

  $ hg init

  $ echo qqq>qqq.txt

rollback dry run without rollback information

  $ hg rollback
  no rollback information available
  [1]

add file

  $ hg add
  adding qqq.txt

commit first revision

  $ hg ci -m 1

set bookmark

  $ hg book test

  $ echo www>>qqq.txt

commit second revision

  $ hg ci -m 2

set bookmark

  $ hg book test2

update to -2 (deactivates the active bookmark)

  $ hg update -r -2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (leaving bookmark test2)

  $ echo eee>>qqq.txt

commit new head

  $ hg ci -m 3
  created new head

bookmarks updated?

  $ hg book
     test                      1:25e1ee7a0081
     test2                     1:25e1ee7a0081

strip to revision 1

  $ hg strip 1
  saved backup bundle to $TESTTMP/.hg/strip-backup/*-backup.hg (glob)

list bookmarks

  $ hg book
     test                      0:5c9ad3787638
     test2                     0:5c9ad3787638